The present invention generally relates to the production of processed semiconductor wafers and, in particular, relates to an apparatus and method for controlling the flow of semiconductor wafers through a wafer processing facility.
In one instance wherein the present invention concept is particularly practical, silicon-on-insulator (SOI) semiconductor wafers are generally subjected to both metrology and chemical etching processes prior to being subjected to thin film patterning processes for circuit formation. During a typical SOl semiconductor wafer metrology process, a metrology instrument measures the thickness of the active material layer of an SO1 semiconductor wafer. This thickness is measured and recorded so that the surface of the SOI wafer may later be thinned and smoothed via a localized chemical etching process. Such a metrology instrument is described in a related patent application entitled, apparatus and Method for Measuring the Thickness of Thin Films, U.S. patent application Ser. No. 07/804,872, filed on Dec. 6, 1991now U.S. Pat. No. 5,333,049. During a typical chemical etching process, a chemical etching instrument induces the removal of specific amounts of material at specific locations along the surface of the SOI semiconductor wafer in order to achieve a desired thickness in the active material layer of the SOI semiconductor wafer. The amount and the location of the removed material is determined from recorded metrology process data. The material is removed as a result of a chemical reaction that occurs between the surface material of the SOI wafer and a plasma generated chemical etchant. Such a chemical etching instrument is described in a related patent application entitled, System for Removing Material from a Wafer, U.S. Pat. application Ser. No. 07/696,897, filed on May 7, 1991, now U.S. Pat No. 5,333,049.
Before the SOI wafer is subjected to either the above-described metrology process or the above-described chemical etching process it must be registered to both the metrology instrument and the chemical etching instrument, respectively, in a consistent manner to ensure that the SOI wafer is properly processed. That is, the position of the SOI wafer in the metrology instrument, and hence the recorded metrology data, must directly correlate with the position of the SOI wafer in the chemical etching instrument, and hence the intensity and location of the material removing chemical reaction. An apparatus for ensuring such consistent registration is described in a related patent application entitled, Apparatus for Providing Consistent Non-Jamming Registration of Semiconductor Wafers, U.S. patent application Ser. No. 07/937,793, filed on Aug. 28, 1992 now U.S. Pat. No. 5,352,249.
As is common in the semiconductor industry, the above-described metrology and chemical etching processes, along with the corresponding wafer registration procedures, must be performed in an atmosphere of extreme cleanliness. Furthermore, these processes must be performed under a high degree of control and accurate records must be kept of the individual wafers before, during, and after the performance of such processes. In a production environment, these requirements are often cosily to maintain with respect to both equipment and labor expenditures. Accordingly, it would be highly desirable to provide a wafer production environment having a high degree of cleanliness and near real time process control while decreasing the cost to maintain such an environment with respect to either equipment or labor or both.